1. Field of the Invention
The present invention relates to a shutter/diaphragm apparatus which serves not only as a shutter but also as a diaphragm (aperture stop) in a camera or the like.
2. Description of the Related Art
A shutter/diaphragm apparatus in which aperture blades can also be used as shutter blades is known in the art. In such a known shutter/diaphragm apparatus, a plurality of blades are provided between an annular diaphragm cam plate and a diaphragm rotation plate, so that a relative rotation between the cam plate and the rotation plate causes the blades to rotate or swing to vary the size of the aperture defined at a central portion of the blades (aperture-stop mechanism) or completely close the aperture (shutter mechanism).
In the above-mentioned known shutter/diaphragm apparatus, to make the shape of the aperture as circular as possible, not only must the number of blades be increased but also each blade must be elongated and smoothly curved in an arc-shape.
However, if the number of blades is increased, it is difficult to overlap the blades at the center of the aperture because the blades interfere with each other at the center of the aperture. Thus, the aperture does not completely close which is not acceptable in a shutter.
To solve this problem, a number of proposals have been made. For example, in Japanese Unexamined Patent Publication No. 4-133038 each blade is provided with an extension which is adapted to completely close the aperture.
However, in the above proposed system, if, for example, five or more elongated blades are partly overlapped, the distal end (end of the aperture side) of the uppermost blade interferes with the base end of the lowermost blade due to a possible deformation or deflection of the blades. Consequently, no appropriate shutter operation can be obtained or the blades may be damaged.
If the number of blades is restricted to provide an appropriate shutter operation, it is difficult to realize an approximately circular aperture as mentioned above, and the aperture is star-shaped or diamond-shaped. Thus, no appropriate diaphragm function can be obtained.